Close contacts to infectious patients with tuberculosis had high rates of tuberculosis, with most disease diagnosed before or within 3 months after the index patient' diagnosis. Contact investigations need to be prompt to detect tuberculosis and maximize the opportunity to identify and treat latent infection, to prevent disease.

Objective To characterize risk factors for non-completion of treatment for latent tuberculosis infection (LTBI). Secondarily, to assess the impact of LTBI treatment regimen on subsequent risk of tuberculosis. Methods Close contacts of adults (≥15 years) with pulmonary tuberculosis were prospectively enrolled in a multi-center study in the U.S. and Canada from January 2002–December 2006. Close contacts to TB patients were screened and cross-matched with tuberculosis registries to identify those who developed active tuberculosis. Results Of the 3,238 contacts screened, 1,714 (53%) were diagnosed with LTBI. Preventive therapy was recommended in 1,371 (80%); 1,147 contacts (84%) initiated therapy, of whom 723 (63%) completed treatment. In multivariate analysis, study site, initial interview sites other than a home or healthcare setting, and treatment with isoniazid were significantly associated with LTBI treatment non-completion. Fourteen tuberculosis cases were identified in contacts, all of whom initiated isoniazid. There were two cases among persons who received six or more months of isoniazid (66 cases/100,000 person-years), and nine cases among persons who received 0–5 months (median 2 months) of isoniazid (792 cases/100,000 person-years; p<0.001); data on duration of isoniazid for three cases were not available. Conclusion Only 53% (723 of 1,371) of close contacts for whom preventive therapy was recommended actually completed treatment. Close contacts of TB patients were significantly less likely to complete LTBI treatment if they took isoniazid. Less than six months of isoniazid therapy was associated with increased risk of active TB.

Background Close contacts of persons with pulmonary tuberculosis (TB) have high rates of TB disease. Methods We prospectively enrolled TB patients and their close contacts at 9 US/Canadian sites. TB patients and contacts were interviewed to identify index patient, contact, and exposure risk factors for TB. Contacts were evaluated for latent TB infection (LTBI) and TB, and the effectiveness of LTBI treatment for preventing contact TB was examined. Results Among 4490 close contacts, multivariable risk factors for TB were age ≤5 years, US/Canadian birth, human immunodeficiency virus infection, skin test induration ≥10 mm, shared bedroom with an index patient, exposure to more than 1 index patient, and index patient weight loss (P &lt; .05 for each). Of 1406 skin test–positive contacts, TB developed in 49 (9.8%) of 446 who did not initiate treatment, 8 (1.8%) of 443 who received partial treatment, and 1 (0.2%) of 517 who completed treatment (1951, 290, and 31 cases/100 000 person-years, respectively; P &lt; .001). TB was diagnosed in 4.2% of US/Canadian-born compared with 2.3% of foreign-born contacts (P = .002), and TB rates for US/Canadian-born and foreign-born contacts who did not initiate treatment were 3592 and 811 per 100 000 person-years, respectively (P &lt; .001). Conclusions Treatment for LTBI was highly effective in preventing TB among close contacts of infectious TB patients. Several index patient, contact, and exposure characteristics associated with increased risk of contact TB were identified. These findings help inform contact investigation, LTBI treatment, and other public health prevention efforts.

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